Method of producing refractory metals



March 11, 1958 G. R. FINDLAY METHOD OF PRODUCING REFRACTORY METALS FiledSept. 10; 1951 3 Sheets-Sheet 1 IN VEN TOR.

I| I- I BY 'GORDON R. FINDLAY Ola/((1 FIG.

ATTORNEY March 11, 1958 G. R. FINDLAY 2,826,491

METHOD OF PRODUCING REFRACTORY METALS FiledSept. 10, 1951 3Sheets-Sheet2 IN VEN TOR BY GORDON R FINDLAY ATTORNEY March 11, 1958 ca. R. FINDLAY1 METHOD OF PRODUCING REFRACTORY METALS Filed Sept 10. 19.51 sSheets-Sheet s 7 80 All)? A(.g. H62 (1) v V S'l'orcige Melering Pump orValve Pressure 46 f lgl.

Relief Valve 48 Argon 1 B 7 j VaporizAalion Bur l4 l jB(g) B (1) Argon J(9 Argon -66 97] t 24 Vaporizer Condensalion l for B of B 98? B (9) FreeAirpressure vacuum 0'50 Microns Argon Press I aim. Pump 69 /89 lMel'ering L l an H Pump B m A Halide 26 .1- 2

( Ingol 68 p Filler tIOO (c.g.Ti) or (2) Ti (powder) V-alve BunEleclrolysis of RH B (e.g. No) B Halide Slorage g CO l 92 Halogen l lSCrude A Formalion of A (e.greacl'ion of Halogen will: C-l-TiOz)Fraclionalion I Au -S+ripper Crude A Purifying ofA l I Column Sl'orageAgenl' 95 l Impurities (e.g. sich) INVENTOR;

Fmid FIG. 3 BY GORDON R. FINDLAY ATTORNEY rvmrnon or rnopnonsonnrnncronv METAES Gordon R. Findlay, Bedford, Mass, assignor to NationalResearch Corporation, Cambridge, Mass, at corporation of MassachusettsApplication eptember 10, 1951, Serial No. 245,873

4 Claims. (Cl. 7584.4)

This invention relates to the production of metals and more particularlyto the production of metals in a high state of purity. This invention isparticularly concerned with improvements in the metal torch process ofthe type described in the application of Gordon R. Findlay, Serial No.200,606, filed December 13, 1950.

A principal object of the present invention is to provide improvedprocesses for the production of metals and alloys thereof, andparticularly high-melting-point metals, such as titanium, zirconium, andthe like, by the reduction of a halide of such metals.

Another object of the invention is to provide for improved heatdissipation in processes of the above type wherein a highly exothermicreduction of the metal halide is achieved by reaction between the metalhalide and an alkali metal or alkali earth metal.

Still another object of the invention is to provide an improvedapparatus for carrying out processes of the above type wherein animproved arrangement is provided for initially starting a reaction byproviding a pool of molten titanium or the like against the surface ofwhich the reaction products are directed.

Another object of the present invention is to provide an apparatus ofthe above type wherein an electrode is employed for initially meltingthe titanium and this electrode is so arranged that it has a long lifedespite the high heat of the reaction during operation of the apparatus.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and the order of one or more of such steps withrespect to each of the others, and the apparatus possessing theconstruction, combination of elements and arrangement of parts which areexemplified in the following detailed disclosure, and the scope of theapplication of which will be indicated in the claims.

For a fuller understanding 'of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings wherein:

Fig. 1 is a diagrammatic, schematic, partially sectional view of onepreferred embodiment of the invention;

Fig. 2 is an enlarged sectional view of a portion of Fig. l; and

Fig. 3 is a flow sheet illustrating one preferred use of the invention.

in general the present invention relates to the productionof metals bythe reduction of a reducible compound thereof. This reducible compoundis preferably one which can be vaporized at a temperature below itsdecomposition temperature and the invention will, for simplicity ofillustration, be initially described in connection with the productionof titanium by the reduction of a titanium tetrahalide by an alkalimetal or alkali earth metal.

The present invention is primarily directed to improvements in the metaltorch process and apparatus of the type described in the above mentionedFindlay applicstion. in this metal torch, titanium tetrachloride, forexample, is introduced, preferably as a vapor, into a reaction zonewithin a reaction chamber which has an atmosphere inert to titanium.This inert atmosphere is preferably an atmosphere of a gas such asargon. The reducing agent, which is also preferably introduced into thereaction zone in vapor phase is, in a preferred embodiment, an alkalimetal such as sodium. The two reactants (i. e., sodium and titaniumtetrachloride) are mixed to gether as they enter the reaction zone theyburn with a highly exothermic reaction to form molten titanium dropletsand sodium chloride vapors as by-products of the reaction. The rate ofintroduction of the two reactants is preferably such that the heat ofthe reaction is sufficient to melt the product titanium and to maintainthe by product sodium chloride in a vapor phase. The reacting gases orvapors are preferably directed towards the molten surface of a titaniumingot so that the product titanium, in liquid form, coalesces on thesurface of the ingot. The: by-product sodium chloride is preferablyseparately con-- densed from the point of collection of the producttita-- nium.

In the above reaction the heat generated is extremely high. Theadiabatic flame temperature has been calcu lated to be on the order of2800 C. However, even when: the refractory metals molybdenum or tungstenare utilized for lining the walls of the reaction chamber, it isundesirable to maintain temperatures as high as 1900 C. at the innersurfaces of these walls, since it is possible for titanium to condenseon these walls and to form a lower melting eutectic with the refractorymetal of the walls. This is due to the fact that some of the producttitanium, even though it is a very small percentage, may not becollected by impingement on the ingot and is free to collect on thewalls of the reaction chamber. As a consequence it is desirable tomaintain the inner wall of the reaction chamber at a temperature belowthe melting point of the eutectic formed between the product titaniumand the refractory metal of the inner wall. This temperature shouldpreferably be maintained close to, but below about, 1465 C. (the boilingpoint of sodium chloride). it is also undesirable to maintain too high atemperature drop through the walls of the reaction chamber due to thethermal stresses to which these walls would be subjected.

In the present invention the refractory metal inner wall in the reactionchamber is maintained at a high temperature on the order of 1465 C., andthe temperature drop through this wall is maintained low by making thiswall quite thin, on the order of inch thick. Thus, even though there isa large heat flux through this wall, the temperature drop and thermalstresses in the wall are maintained at a minimum. In order to removethis high heat of reaction the heat passing through the inner wall istransmitted to the outer wall substantially entirely by radiation. Thisradiation heat transfer thus permits the great majority of thetemperature drop to take place in the space between the inner wall andthe outer wall. Thus the outer Wall may be maintained at a considerablylower temperature, on the order of 800 1000" 0., this outer wall beingcooled by having a liquid heat-exchange medium in contact with the outersurface thereof. To prevent destructive oxidation of the inner wall, thespace between the inner wall and the outer wall is preferably filledwith inert gas such as argon, the pressure of this gas being such as toequalize the pressure within the reaction chamber so that there isessentially no mechanical stress applied to this inner walL. In order toincrease the radiant heat between the outer surface of the inner walland the inner surface of the outer wall, these surfaces are treated togive them a high emissivity on the order of about .9. This may beachieved by first coating these surfaces wtih chromium and thenoxidizing the chromium. Such chromium oxide surfaces are capable oftransferring well above 100,000 B. t. u. per square foot per hour byradiation if operating between a temperature level of 1465 C., and 1090"C.

The above described double wall construction for the reaction vesselprovides a gas-tight reaction vessel whose inner surface can besubjected to high temperature radiation, and which can be maintained ata relatively high temperature without being destroyed. This reactionvessel is also capable of removing extremely large quantities of heatfrom the reaction chamber without subjecting either of the Walls of thereaction chamber to undue thermal stresses.

The present invention also includes a provision for are melting thesurface of an ingot of titanium positioned within the reaction chamberprior to starting of the reaction. This is of particular importance inpermitting the reaction to achieve a steady state very shortly afterbeing started, and provides for high collection efficiency of theproduct titanium from the beginning of the reaction. In the preferredembodiment of the illustrated construction, the electrode used for aremelting the surface of the titanium ingot is so arranged that when thereaction is started this electrode is withdrawn to a position Where itis completely protected from the high temperature of the reaction flame,and is maintained at a relatively low temperature by the flow of one ofthe reactant gases therepast.

Referring now more specifically to Figs. 1 and 2 there is shown oneschematic, diagrammatic illustration of a preferred metal torchembodying the present invention. The apparatus comprises a reactionvessel 16 defining therewithin a reaction chamber 12, this reactionchamber being generally of the type described in the above mentionedFindlay application. Surrounding reaction vessel there is preferablypositioned a second vessel 14, the space 16 between these two vesselsbeing arranged to hold a heat-exchange medium 18. Near the bottom of thereaction chamber 12 there is located an ingot-forming mold 20 in which atitanium ingot 21 is formed during the reaction.

For obtaining intimate mixture of the titanium tetrachloride and sodiumvapors there is provided a torch 22 which separately feeds these twovapors into the reaction chamber and directs these two vapors togetheras they enter the chamber so as to form a flame 23 in which thereduction takes place. This flame 23 serves as the reaction Zone andachieves complete reduction of the titanium tetrachloride to metallictitanium. Since the flame 23 is directed towards the ingot mold 20, theresultant titanium droplets are caused to impinge on the molten surfaceof an ingot in the mold and to coalesce on this surface, the flame beingsuificiently hot to maintain at least the upper surface of the ingot inmolten condition.

The reaction chamber 12 includes a vacuum pumping port 24 connected to asuitable vacuum pumping system (not shown) which can evacuate thereaction chamber 12 to a low free air pressure on the order of less than.001 mm. Hg abs. Located near the bottom of the reaction chamber, andspaced to one side of the ingot mold, is an outlet pipe 26 for removingLiquid sodium chloride 27.

The vapor pressure of the heat-exchange medium 18 is controlled by apressure relief valve, generally indicated at 28, the setting of thispressure relief valve 28 controlling the temperature of the liquidheat-exchange medium 18 as a function of the vapor pressure of the space16a thereabove.

The torch 22 comprises, in the preferred form shown, an outer nozzle 30,through which sodium vapors are adapted to be introduced, an innernozzle 32, through which titanium tetrachloride vapors are introduced,and

an intermediate nozzle 34, through which an inert gas such as argon isintroduced. The inner nozzle 32 may also include an electrode 36 which,when moved to the dotted line position shown in Fig. 1, may be employedfor initially melting the surface of the ingot 21.

As shown in greater detail in Fig. 2, the torch nozzle is preferablyformed of a first tube 38, a second tube 40, and a third tube 42, thesetubes being arranged concentrically. The sodium vapors enter betweentubes 38 and 4t titanium tetrachloride vapors pass through the innertube 42, and the argon passes between tubes 40 and 42. The sodium vaporsare introduced into the torch nozzle through a pipe 44- from a suitablevaporizer, while the titanium tetrachloride vapors are introduced from apipe 46 connected to a suitable supply thereof. Pipe 48 is employed forintroducing the argon into the torch nozzle. A suitable oil-coolingjacket 50 is provided near the top of the torch assembly, while awater-cooling jacket 52 is provided for cooling the electrode 36. Thenozzle in the electrode assembly also includes suitable insulatingsupport members 54 and appropriate electrical connections (not shown). Asuitable power source, such as a welding generator, is preferablyprovided for furnishing power to the electrode 36. This generator ispreferably connected to the electrode 36 so that the electrode isnegative with respect to the titanium ingot to be melted.

The electrode assembly preferably includes a vacuum seal 56 which maycomprise an 0 ring arranged to slide on the inner surface 58 of the oiljacket 50. By this arrangement the O ring 56 and insulating members 54support the electrode as it is moved down to its operative position.They also maintain the electrode positioned concentrically with respectto the nozzle 32 so that the titanium tetrachloride vapors flowing outof the nozzle 32 are evenly distributed around the circumference of theelectrode tip.

The wall 10 of the reaction chamber is preferably made with a doublewall construction, the inner wall 60 comprising a thin refractory metalshell and the outer wall 62 comprising a stainless steel shell. Thefacing surfaces 60a and 62a (see Fig. 2) of these two walls arepreferably treated so as to have a high thermal emissivity and the space64 therebetween is filled with an inert gas such as argon or the like,the pressure of which may be controlled by means of a pipe 66. Thisinert gas pressure is preferably maintained equal to the total pressurewithin the reaction chamber so that there is no pressure drop acrosswall 6i).

In a preferred embodiment of the invention the liquid heat-exchangemedium 18 is sodium which is introduced into the space 16 by means of apipe 68. The sodium preferably enters through pipe 68 at a lowertemperature than the remainder of the sodium 18 in the space 16 so thatthis entering sodium removes heat from the walls of the mold 20 at avery high rate, thus maintaining a solid titanium interface at theinterior surface of the ingot mold. Liquid sodium may be withdrawn fromthe space 16 by means of a pipe 69. A pair of withdrawal rolls 70 isprovided for removing ingot 21 from the reaction chamber. A reducing dieseal '71 may be provided for creating a vacuum-tight seal with the ingotbeing withdrawn from the mold. if desired, seal 71 may be replaced by asleeve-type seal and the mold 29 may be supported on a hydraulic pistonas illustrated in the copending application of Findlay, Serial No.235,535, filed July 5, 1951, now Patent No. 2,709,842 issued June 7,1955. In this modification of the invention the mold 26 is made with aslight taper so that the hydraulic force generated in the mold supportis a direct function of the amount of titanium in the mold. Thishydraulic force can be used to control a variable speed motor so as tospeed up or slow down the withdrawal rolls to maintain the level of themolten metal in the mold substantially constant.

The preferred operation of the device of Fig. 1, and the arrangement ofthe auxiliary equipment, is illustrated best in the flow diagram of Fig.3 wherein like numbers refer to like elements in the other figures. Inthis Fig. 3 there is provided a storage chamber 80 for holding thereducible metal compound A (e. g., titanium tetrachloride). A supplytank for holding the molten metallic reducing agent B (e. g., sodium) isindicated at 82. A pump or valve 84 is included for feeding the titaniumtetrachloride from the supply 80 to a vaporizer 86 therefor, while apump or valve 88 is included for transferring molten sodium from supply82 to the space 16 surrounding the reaction vessel 10. From space 16,sodium may be transferred, by means of a metering pump 89, to a sodiumvaporizer 96, the sodium vapors then passing into pipe 44.

The sodium chloride reaction product in pipe 26 passes through a filter100 to an electrolysis chamber 90. Any titanium particles which do notcollect on the titanium ingot are recovered by the filter 100 andreprocessed to titanium tetrachloride or melted in an arc furnace. Thesodium formed in electrolysis chamber 90 is piped to supply 82 through afilter 91 for removing impurities such as oxides. The chlorine generatedin chamber 90 is piped to a reaction vessel 92 in which the titaniumtetrachloride is formed by reaction with titanium dioxide and carbon.This manufacture of titanium tetrachloride is well described in chapter17 of Titanium, Its Occurrence, Chemistry and Technology, by Barksdale,published (1949) by the Ronald Press Company, New York. The resultantcrude titanium tetrachloride is then piped to a crude storage tank 93 atwhich point a purifying agent such as oleic acid may be added. From thecrude storage tank the crude titanium tetrachloride goes to a stripper 4where some impurities, such as silicon tetrachloride, are removed. Itthen passes through a fractionation column 95', and the thus purifiedtitanium tetrachloride is then pumped to a storage chamber 80.

For initially heating the sodium in the space 16 to a high temperatureon the order of 1000 C., there may be provided a separate heater (notshown), the vapors of the sodium condensing at the top of the space 16and the condensed sodium being recirculated through the heater until thesodium in space 16 has been brought up to the desired temperature. Theinner reactor wall may, if desired, be brought up to operatingtemperature by heat received from the are by radiation. A separatecondenser 9'7 for unreacted sodium may be provided in the vacuum pumpingline 24 leading to a vacuum pumping system schematically indicated at98.

In the operation of the device shown in Figs. 1, 2 and 3, the supplychambers 80 and 82 are filled with titanium tetrachloride and sodium,respectively, some of the sodium being fed to the space 16 so as to fillthis space to the level indicated. This sodium in space 16 may then beheated to a relatively high temperature on the order of about 1000 C.During this heatup time the reaction chamber 12 is preferably evacuatedby means of vacuum pump 98 to a free air pressure on the order of lessthan about 1 micron Hg abs. In lieu of evacuating chamber 12 it may bepurged of air by sweeping with argon introduced through pipes 78 and 48at a pressure slightly in excess of atmospheric pressure. When most ofthe air has been removed from the reaction chamber the electrode 36 maybe moved from the full line position of Fig. 1 to the dotted lineposition, and a suitable power supply may be energized so that the uppersurface of the ingot 21 in the mold 20 is melted.

When the reaction chamber 12 has been brought up to a desired hightemperature, the feed of argon through the pipe 48 is commenced and theelectrode 36 is returned to the full line position. Sodium is thenpumped into the vaporizer 96 and titanium tetrachloride is pumped intothe vaporizer 86. The vapors from these two Vaporizers are fed throughtheir respective nozzles into the reaction chamber. As explainedpreviously, the so= diurn enters through the outer nozzle 30 while thetitanium tetrachloride enters through the inner nozzle 32. A thinblanket of argon passes from the end of nozzle 34 between the titaniumtetrachloride and sodium vapors to prevent interdiffusion of these twovapors until they have passed a short distance into the reactionchamber.

The reactant vapors passing from the torch into the reaction chamberignite with a highly exothermic reaction to give an intensely hot flame23 in which the sodium completely reduces the titanium tetrachloride tometallic titanium with sodium chloride as a lay-product. In order toassure this complete reduction it is preferred that a slight excess ofsodium over the stoichiometric quantity be provided in the sodium vaporfeed. The reaction flame is directed against the top of the titaniumingot and maintains the upper surface of this ingot in molten condition.The high velocity of the reactant gases, and the consequent highvelocity of the liquid titanium droplets formed in the reaction flame,achieves high impingement separation of the titanium droplets bycoalescing thereof upon the surface of the molten titanium ingot.

Since the temperature of the flame 23 is extremely high, the by-productsodium chloride remains in vapor phase in the reaction zone and issubstantially completely separated from the metallic titanium formed inthe flame. The sodium chloride 27 is preferably condensed on the wallsof the reaction chamber, the sodium chloride running down these Wallsand being withdrawn from the reaction chamher by means of pipe 26.

In the present invention, tne heat of condensation of the sodiumchloride is removed by radiation heat transfer from the inner wall 6% tothe outer wall 62. The facing surfaces of these two walls are preferablyso treated as to have high emissivities on the order of .85 to .9. Inthe preferred construction, inner wall 60 is formed of molybdenum havinga thickness on the order of inch while the outer wall 62 is formed of /8inch stainless steel. The facing surfaces of these walls are then givena coating of chromium oxide, for example, so that they have emissivitiesof about .85 or more. When the inner wall 6%? is maintained attemperatures of about 1465 C. (the boiling point of sodium chloride)approximately 144,000 B. t. u. per square foot per hour can betransferred from the reaction chamber. Thus an inner wall area of 10square feet is ample to transmit the approximately 1,100,000 B. t. u.per hour required for a titanium production rate of 120 pounds per hour.

With the preferred construction described above the temperature dropthrough each of the walls 60 and 62 is maintained very low, well lessthan 100 C., while the majority of the temperature drop (on the order of400 C.) is maintained between the walls. This arrangement has theparticular advantage, in addition to the advantage of high heat transferwith low thermal stress, of preventing the creation of hot spots on theinner wall. This is due to the fact that the amount of heat transferredby radiation increases as the fourth power of the temperature. Thus, anytemporary increase in the temperature of a portion of the inner wallimmediately and enormously increases the radiation heat transfer fromthis hotter portion, thereby rapidly cooling it to the designtemperature. Since the outer wall 62 has essentially the sametemperature as the liquid sodium in the space 16 (plus a few degrees forthe temperature drop through wall 62), the amount of heat transferred byradiation from the inner wall can be maintained essentially constant bycontrolling the vapor pressure, and thus the temperature, of the liquidsodium. I

The withdrawn sodium chloride passes to the electrolysis chamber whereit is electrolyzed, by usual techniques, to sodium and chlorine. Theresultant sodium is recirculated to the sodium supply 82 while thechlorine is passed to the reaction chamber for forming titaniumtetrachloride by reaction with carbon and titanium dioxide.

seesaw This titanium tetrachloride is then purified and fed to thetitanium tetrachloride supply 80. Any unreacted sodium is condensed incondenser 97 and fed back to the sodium supply 82. The argon passing outof the reaction chamber with any unreacted sodium vapors may beseparated in the condenser 97 and recycled through the system.

During the build-up of metallic titanium in the mold 20, by theimpingement of freshly formed titanium droplets on the surface of theingot therein, the mold walls are kept below the melting point oftitanium by the feed of the heat-exchange medium in contact with theouter surface of these mold walls. The level of the molten titanium inthe mold is preferably maintained essentially constant by withdrawingthe ingot 21 by means of rolls 70 as titanium is added to the ingot.This rate of withdrawal may be controlled by thermocouples positioned inthe mold wall or by other means, such as means for measuring thewithdrawal force, for indicating the level of the molten titanium in themold. When visual means are employed it is preferred to use asniperscope which will be affected only by radiation in the infrared soas to eliminate, as far as possible, the scattering of light bycondensed smoke particles of sodium chloride in the reaction chamber.

While one preferred embodiment of the invention has been describedabove, wherein substantially all of the sodium chloride by-product iscondensed within the reaction chamber, it is equally feasible tocondense only a small portion (or none) of this sodium chloride in thereaction chamber and to condense most of the sodium chloride vaporsoutside of the reaction chamber. Such condensation may be achieved byquenching with a cooler liquid, such as a fused salt mixture of sodiumand calcium chlorides. This modification of the invention is fullydescribed in the copending application of Benedict and Pindla Serial No.244,138, filed August 29, 1951, now abandoned.

Additionally, the present invention is of wide utility for processes andapparatus useful in the manufacture of numerous materials other thantitanium. One such alternate process is the reduction of zirconiumtetrachloride by sodium or magnesium. These alternative processes areset forth fully in the above mentioned copending application of Findlay,Serial No. 200,606. As described fully in this copending Findlayapplication, the basic metal torch" process can be utilized for making anumber of metals or alloys, particularly the group lVa and Va metals (i.e., titanium, zirconium, hafnium, vanadium, columbium, and tantalum).

When alloys are to be made with the apparatus described above, thealloying element can be added in solid form to the ingot being formed inthe mold 2ft. This may be done very conveniently by replacing electrode36 with a rod of the alloying metal. This is particularly desirable whenmost of the reducible compounds of such alloying metals have low vaporpressures. When a rod of the alloying element is fed into the reactionchamber in place of the electrode d6, the alloying element is melted inthe flame of the reactor and drips into the molten titanium in the ingotmold. in this case, the alloying element is fed at a rate adiusted tothe rate of titanium production. If desired, this rate of rod feed canbe controlled by the rate of ingot Withdrawal or by the rate of titaniumtetrachloride feed, for example.

Additionally, the present invention can make the product metal in theform of a powder or a partially sintered mass. Equally, while it ispreferred that a single reducing agent used, it is possible, andsometimes desirable, to use a mixture of two reducing agents so that theby-product halide is a mixed halide which, for some purposes, may have adesirably low melting point. The present invention has great utility inof these modifications of the metal torch invention.

While the present invention has been described primarily in connectionwith the removal of heat from the reaction chamber, it may be equallyapplied to the condensation of the sodium vapors in condenser 97 (Fig.3). In this case the sodium vapor condenser may comprise a helical coil(for example) whose outer surface is blackened to increase itsemissivity. This coil is placed between two water-cooled shells (alsoblackened) so that heat radiates from the coil (at 400 C. to 1000 C.) tothe two shells (at about 100 C.). The space surrounding the coil isfilled with an inert gas such as argon so that there will be no dangerof oxidation of the coil at its relatively high operating temperature.With such an arrangement sodium vapors (at about 1000 C.) are fed intothe top of the coil and liquid sodium (at about 400 C.) is withdrawnfrom the bottom of the coil. Obviously, if desired, the liquid sodiummay be withdrawn at a lower or higher temperature, depending upon itsuse thereafter. Equally, the water jackets can be operated attemperatures above 100 C. to generate steam for heat exchange or poweruse. If desired, such a water jacket, separated by aradiation-transmitting space, can be provided outside of outer wall 14of the reaction chamber so that the heat of the reactor can be convertedinto hot water or steam. In this case, a relatively small amount ofsodium vapors would be generated in the space 16.

In connection with all of the above embodiments of the invention, theradiation heat transfer from the hot surface to the cooler surface canbe controlled by interposing radiation reflectors between these surfacesto cut down the transfer of radiant heat. Such shields are particularlyuseful when it is desired to operate the inner wall 60, for example, ata higher temperature. Such flexibility of operation is particularlydesirable for producing a Wide range of diiferent alloys or differentmetals in a single reaction chamber and permits use of a wide choice ofreducible metal compounds and reducing agents.

The flow of heat by radiation from the inner reactor wall 60, forexample, to the outer wall 62 can be readily varied by changing thetemperature of the outer wall when the temperature difference betweenthese walls is at a relatively low amount, such as 150 C. This is due tothe fact that the heat transferred by radiation is expressed by thefollowing formula:

e =ernissivity of radiator e =emissivity of receiver T =temperature ofthe radiator R) T =temperature of the receiver R) Q heat transferred (B.t. u./hr./ft.

When the temperature difference is small a relatively small change inthe temperature of the cooler surface can exert a great change in theamount of heat transferred thereto from the hotter surface. When thehotter surface is to be maintained at about 1465 C., for example, andcareful control is desired, even though the heat generation in thereactor is widely changed from optimum design conditions this controlcan be achieved by utilizing a heat-exchange medium which has arelatively lower vapor pressure than sodium. Thus the temperature ofthis heat-exchange medium can be conveniently raised to a temperaturenot much below the temperature of the inner wall. Thus, if the relativeareas and emissivities require the outer wall to be at a temperature ofabout 1300 C. this may be readily achieved by using magnesium as theheat-exchange medium 18 and maintaining its vapor pressure at about 42pounds/in. absolute. With sodium as the heat-exchange medium a where:

pressure of about pounds/in. absolute would be required to maintain atemperature of 1300 C.

Numerous types of high-emissivity surfaces may be employed in thepresent invention. Among these are chromium oxide, blueing (for lowtemperature use), iron oxide, nickel oxide, and various complex mixturesof these and other oxides.

In connection with the above described modifications of the invention,where heat is transferred by radiation from sodium at about 1000 C. towater at about 100 C., it should be pointed out that the presentinvention has the additional, and extremely important, advantage that aleak in either the sodium-confining wall or the waterconfining wall willnot permit any mixing of sodium and water. The leaks would have todevelop simultaneously since it is relatively simple to detect thepresence of either sodium or water in the space between these walls byoptical, electrical or chemical means. Thus the present invention, whenapplied to the condensation of one material by heat exchange with asecond material which is highly reactive with the first material,provides a factor of safety not found in usual condensers.

Since certain changes may be made in the above process and apparatuswithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description, or shown inthe accompanying drawings, shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:

1. In a process for producing a product metal selected from the groupconsisting of titanium, zirconium, hafnium, vanadium, columbium,tantalum and mixtures thereof by reduction of a halide of the productmetal with a metallic reducing agent selected from the group consistingof lithium, sodium, potassium, magnesium and calcium, the improvementwhich comprises mixing at least one halide and the reducing agent eachin fluid phase in a reaction zone in a reaction chamber having an innermetallic wall and an outer wall, the introduced halide and reducingagent reacting with intense heat to form a highly heated reaction flamewhich is at a temperature above the melting point of the product metaland above the vaporization temperature of the by-product halide,directing said flame against a body of the product metal to maintain thesurface of the product metal at an elevated temperature above thevaporization temperature of the by-product halide and to collect theproduct metal in the flame on the hot product metal surface, theelevated temperature being due substantially to the reaction heat andthe superheat of the reactants,'separately withdrawing the product metaland the by-product halide from the reaction zone, maintaining the innerwall of the reaction chamber adjacent the reaction zone at a temperaturebetween the melting point of the by-product halide and the melting pointof any eutectic formed between the product metal and the metal of theinner wall, and transferring heat from the inner Wall to the outer wallprimarily by radiation.

2. In a process for producing a group IV metal from the class consistingof titanium and zirconium by reduction of a group IV metal tetrahalidewith a metallic re ducing agent from the group consisting of the alkalimetals and the alkaline earth metals, the improvement which comprisesmixing vapors of the tetrahalide and vapors of the reducing agent in areaction zone in a reaction chamber having an inner metallic wall and anouter wall,

the introduced halide and reducing agent reacting with intense heat toform a highly heated reaction flame which is at a temperature above themelting point of the group IV metal and above the vaporizationtemperature of the by-product halide, directing said reaction flameagainst the surface of the group IV metal body to maintain said surfacemolten by transfer of heat from the flame to the surface and to collecton the molten group IV metal surface liquid group IV metal carried inthe flame, simul taneously removing heat from the group IV metal body tosolidify liquid group IV metal at the solid-liquid interface, separatelywithdrawing the product group IV metal and the by-product halide fromthe reaction zone, maintaining the inner wall of the reaction chamberadjacent the reaction zone at a temperature between the melting point ofthe by-product halide and the melting point of any eutectic formedbetween the product metal and the metal of the inner wall, andtransferring heat from the inner wall to the outer wall primarily byradiation.

3. The process of claim 1 wherein the inner surface of the inner wall ismaintained at a temperature such that it is substantially completely wetby condensing the byproduct halide as a liquid thereon.

4. The process of claim 1 wherein a protective atmosphere is maintainedbetween the inner and outer walls, the total pressure of the protectiveatmosphere being essentially the same as the total pressure inside ofthe reaction chamber.

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1. IN A PROCESS FOR PRODUCING A PRODUCT METAL SELECTED FROM THE GROUPCONSISTING OF TITANIUM, ZIRCONIUM, HAFNIUM, VANADIUM, COLUMBIUM,TANTALUM AND MIXTURES THEREOF BY REDUCTION OF A HALIDE OF THE PRODUCTMETAL WITH A METALLIC REDUCING AGENT SELECTED FROM THE GROUP CONSISTINGOF LITHIUM, SODIUM, POTASSIUM, MAGNESIUM AND CALCIUM, THE IMPROVEMENTWHICH COMPRISES MIXING AT LEAST ONE HALIDE AND THE REDUCING AGENT EACHIN FLUID PHASE IN A REACTION ZONE IN A REACTION CHAMBER HAVING AN INNERMETALLIC WALL AND AN OUTER WALL, THE INTRODUCED HALIDE AND REDUCINGAGENT REACTING WITH INTENSE HEAT TO FORM A HIGHLY HEATED REACTION FLAMEWHICH IS AT A TEMPERATURE ABOVE THE MELTING POINT OF THE PRODUCT METALAND ABOVE THE VAPORIZATION TEMPERATURE OF THE BY-PRODUCT HALIDE,DIRECTING SAID FLAME AGAINST A BODY OF THE PRODUCT METAL TO MAINTAIN THESURFACE OF THE PEODUCT METAL AT AN ELEVATD TEMPERATURE ABOVE THEVAPORIZATION TEMPERATURE OF THE BY-PRODUCT HALIDE AND TO COLLECT THEPRODUCT METAL IN THE FLAME ON THE HOT PRODUCT METAL SURFACE, THEELEVATED TEM PERATURE BEING DUE SUBSTANTIALLY TO THE REACTION THESUPERHEAT OF THE REACTANTS, SEPARATELY WITHDRAWING THE PRODUCT METAL ANDTHE BY-PRODUCT HALIDE AND ACTION ZONE, MAINTAINING THE INNER WALL OF THEREACTION CHAMBER ADJACENT THE REACTION ZONE AT A TEMPERATURE BETWEEN THEMELTING POINT OF ANY EUTECTIC FORMED BETWEEN THE THE MELTING POINT OFANY EUTECTIC FORMED BETWEEN THE PRODUCT METAL AND THE METAL OF THE INNERWALL, AND TRANSFERRING HEAT FROM THE INNER WALL TO THE OUTER WALLPRIMARILY BY RADIATION.